Learning image from projection: a full-automatic reconstruction (FAR) net for sparse-views computed tomography

Abstract: The sparse-views x-ray computed tomography (CT) is essential for medical diagnosis and industrial nondestructive testing. However, in particular, the reconstructed image usually suffers from complex artifacts and noise, when the sampling is insufficient. In order to deal such issue, a full-automatic reconstruction (FAR) net is proposed for sparse-views CT reconstruction via deep learning technique. Different with the usual network in deep learning reconstruction, the proposed neural network is an End-to-End network by which the image is predicted directly from projection data. The main challenge for such a FAR net is the space complexity of the CT reconstruction in full-connected (FC) network. For a CT image with the size $N \times N$ , a typical requirement of memory space for the image reconstruction is $O(N^{4})$, for which is unacceptable by conventional calculation device, e.g. GPU workstation. In this paper, we utilize a series of smaller FC layers to replace the huge based on the sparse nonnegative matrix factorization (SNMF) theory. By applying such an approach, the FAR net is able to reconstruct sparse-views CT images with the size $512\times 512$ on only one workstation. Furthermore, a Res-Unet structure is composed in the FAR net for suppressing the artifacts and noise caused by under-sampling data. The results of numerical experiments show that the projection matrix and the FAR net is able to reconstruct the CT image from sparse-views projection data with a superior quality than conventional method such as FBP and optimization based approach. Meanwhile, the factorization for the inverse projection matrix is validated in numerical.